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Uncovering the causes of male infertility in fish

The discovery of a new hormonal mechanism that controls the formation of spermatozoa in fishes could help to explain the causes of male infertility in fish.

 

The LH hormone receptor (red and green) in the spermatids (germ cells which will transform into spermatozoa) of Senegalese sole, zebrafish and gilthead seabream. Until now, it was believed that vertebrate spermatids do not have the LH receptor.One of the unsolved questions in the aquiculture of the flatfish Senegalese sole is to find out why males raised in captivity are infertile. This is an important drawback for the sustainable development of the aquaculture of this species. Some hypothesis have been recently proposed.

According to one of them, male infertility could be related to epigenetic effects  during the development of the larvae, which causes are unknown. Another hyphotesis suggests as a possible explanation the impaired communication with females, due to some deficiency in brain development. Another possibility is some problem in the testis, which will result in the production of low quality sperm. In any case, the causes of the infertility of captive male sole is still a mystery.

A scientific work led by Joan Cerdà, IRTA scientist at the Instituto de Ciencias del Mar (ICM-CSIC), reports a new hormonal mechanism that controls the formation of spermatozoa in fishes which could help to explain the mystery. The work has been recently published in the Proceedings of the National Academy of Sciences (PNAS) magazine.

The research could offer new technologies in the future, such as the in vitro production of spermatozoa, which would be interesting for aquiculture and the conservation of endangered species

The researchers have found a new role of the luteinizing hormone (LH) in the germinal cells of the Senegalese sole. It is accepted that the formation of spermatozoa in vertebrates occurs in response to androgens (male hormones) produced by the somatic Leydig cells present in the testes. The androgens are produced after the activation of the LH receptor, also called choriogonadotropin receptor (LHCGR), by LH in these cells, and they control the transformation of germinal cells into spermatozoa (spermiogenesis).

Cerdà and colleagues have seen that late germinal cells of The Senegalese sole express also the receptor LHCGR, which is activated by LH hormone and directly drives spermiogenesis.

This finding uncovers a new role of the LH hormone in the germ cells of vertebrates, in which a cascade of signaling events in haploid spermatids activated by the receptor drives gene expression and the transformation of these cells into spermatozoa.

This mechanism, unknown until now, opens new areas of research to decipher the causes of infertility in male Senegalese sole, but also for other species, as “low fertilization success in captivity affects other flatfishes”, says the scientist Joan Cerdà. In addition, points out Cerdà, “we have also found that in other fishes such as the gilthead sea bream or the zebrafish, which are not flatfishes, some of the germ cells of the testis also express the LH hormone receptor. Therefore, our findings could be general, at least, for fish”.

Finally, this research could offer new technologies in the future, such as the in vitro production of spermatozoa, which would be interesting for aquaculture and the conservation of endangered species.

Chauvigné F, Zapater C, Gasol JM, Cerdà J. 2014. Germ-line activation of the luteinizing hormone receptor directly drives spermiogenesis in a nonmammalian vertebrate. Proc Natl Acad Sci U S A. 111(4):1427-1432.